In a display device such as a cathode ray tube, a vacuum fluorescent display, a plasma display panel, or the like, a colored transparent conductive film is formed on an outside surface of a transparent front panel (which means, for example, a panel in the case of the cathode ray tube), for the purpose of achieving high contrast, electromagnetic wave shielding, and so on, and a transparent film having a low refractive index is further formed on the colored transparent conductive film, thereby providing an antireflection function.
Conventional conductive films formed for an antistatic purpose need only have a surface resistance at a level of about 1×105 Ω/□, while the conductive films formed for the purpose of electromagnetic wave shielding are required to have a surface resistance as low as at most 1×104 Ω/□, and even at most 1×102 Ω/□.
In recent years, control on a color tone of a transmitted image by a surface treatment of a transparent substrate is becoming more advantageous in terms of cost and others than control on a color tone of a transmitted image by a transparent substrate itself. Therefore, there are increasing trends to provide a color tone control function by coloring a transparent conductive film.
Colored transparent conductive film having these functions are formed by applying a liquid containing dispersed fine particles of a noble metal such as gold, platinum, silver, palladium, or the like. However, gold, platinum, and palladium are expensive, and silver is low in chemical resistance to hydrochloric acid, a salt solution, and so on. For these reasons, proposals have been made to adopt a colored transparent conductive film using ruthenium.
Actually, use of ruthenium only raises a problem that the color tone of the transmitted image is not neutral, because its transmittance is low in a short wavelength region of visible light. Thus, it is necessary to compensate the color tone with a large amount of a complimentary-color material. However, the use of the complimentary-color material resulted in posing, in turn, problems of decrease in the electromagnetic wave shielding performance due to increase of the surface resistance, increase in the cost, degradation of abrasion resistance and chemical resistance, and so on.
It is an object of the present invention to provide a coating liquid for forming a colored transparent conductive film using fine particles of ruthenium, which can form a colored transparent conductive film having a satisfactory electromagnetic wave shielding effect, being excellent in transparency, chemical resistance, and abrasion resistance, and achieving neutral transmitted color tone. It is another object of the present invention to provide a substrate with the colored transparent conductive film and a method for its production, and a display device having the substrate as a front panel.